David Cameron has defended British arms sales to Gulf countries as "entirely legitimate" but insisted that the Arab spring was a positive development and there were no "no-go areas" in talks with autocratic allies who are fretting about changes elsewhere in the region.

Speaking on the first day of a three-day middle east tour, the prime minister rebuffed critics unhappy with the idea of UK defence exports and said his discussions in the United Arab Emirates and Saudi Arabia, both irritated by rows with Britain, would show "respect and friendship".

The trip is aimed at drumming up business in both countries for BAE Systems, the defence manufacturer. An important BP oil deal in Abu Dhabi has run into trouble recently.

Thirty thousand jobs in the UK were at stake, sales were "legitimate and right" and his purpose was "to help Britain compete and thrive in the global race" he said. Cameron wants to persuade the UAE to buy Eurofighter Typhoons to replace their ageing fleet of French Mirage jets. The Emiratis have expressed interest in ordering 60 jets. Oman has expressed interest in 12, while the Saudis are considering a second order on top of the 72 they already have.

Amnesty International criticised what it described as a "deeply-disturbing trade-off" between trade and strategic interests and the promotion of rights and democratic reform. The Campaign Against the Arms Trade condemned what it called "a very clear UK message of support for these authoritarian regimes". Promoting arms sales meant concerns about human rights were "empty words," it added.

Speaking to students in the UAE's capital, Abu Dhabi, Cameron said: "I'm a supporter of the Arab spring, the opportunity of moving towards more open societies, more open democracies, I think is good for the Middle East, for North Africa."

But the UAE's minster of foreign affairs issued a thinly-veiled rebuke as he accompanied Cameron to an airfield to see a display of RAF Typhoons. "Many people are still caught in the euphoria of the Arab spring," said Anwar Gargash. "But in reality what we're seeing currently is basically an entrenchment of conservative religious parties. They're taking control."

The two countries have clashed privately in recent months over criticism in the UK media of the treatment of Islamists in the UAE. It and other conservative Gulf countries are unhappy with the rise of the Muslim Brotherhood during the last two years of change across the region.

The Saudis object to a parliamentary inquiry into UK relations with them and Bahrain. British government officials are aware of the need to balance military and economic interests in what Downing Street called "two of Britain's most important strategic allies in the Gulf" with political and human rights concerns.

Both parties fear Iran's nuclear programme and regional ambitions. Cameron said he believed Tehran was trying to develop nuclear weapons which he said would make the Middle East "a more unstable and more dangerous place".

Amnesty International UK's head of policy and government affairs Allan Hogarth said: "Selling arms to countries like Saudi Arabia and UAE should only be considered if there are absolutely watertight guarantees over them not being used to commit human rights violations.

"Saudi Arabia has been the recipient of record-breaking arms deals involving the UK, yet these have been highly secretive and there's been little or no follow-up over how the weaponry was used."

In 2009 the Saudi air force used UK-supplied Tornado fighter-bombers in attacks in Yemen which killed hundreds – possibly thousands – of civilians. "In the past a large Saudi chequebook has apparently meant it could purchase weapons as well as silence over its own dreadful human rights record. It's time for David Cameron to end this deeply disturbing trade-off."

The prime minister's official spokesman said: "We do have a large and important defence industry in this country. The prime minister is keen to see that industry prosper. That is an important thing for jobs in this country. We have very strict rules, which are regularly reviewed, on the export of defence equipment."